Electrochemical cells are energy conversion devices, usually classified as either electrolysis cells or fuel cells. A proton exchange membrane cell can function as a hydrogen generator by electrolytically decomposing water to produce hydrogen and oxygen gas, and can function as a fuel cell by electrochemically reacting hydrogen with oxygen to generate electricity. Referring to FIG. 1, which is a partial section of an exemplary embodiment of an anode feed electrolysis cell 100, process water 102 is fed into cell 100 on the side of an oxygen electrode (anode) 116 to form oxygen gas 104, electrons, and hydrogen ions (protons) 106. The reaction is facilitated by the positive terminal of a power source 120 electrically connected to anode 116 and the negative terminal of power source 120 connected to a hydrogen electrode (cathode) 114. The oxygen gas 104 and a portion of the process water 108 exit cell 100, while protons 106 and water 110 migrate across a proton exchange membrane 118 to cathode 114 where hydrogen gas 112 is formed.
Another exemplary embodiment of a water electrolysis cell using a configuration similar to the one shown in FIG. 1 is a cathode feed cell, wherein process water is fed on the side of the hydrogen electrode. A portion of the water migrates from the cathode across the membrane to the anode where hydrogen ions and oxygen gas are formed due to the reaction facilitated by connection with a power source across the anode and cathode. A portion of the process water exits the cell at the cathode side without passing through the membrane.
A fuel cell also uses a configuration similar to the one shown in FIG. 1. Hydrogen gas is introduced to the hydrogen electrode (the anode in fuel cells), while oxygen, or an oxygen-containing gas such as air, is introduced to the oxygen electrode (the cathode in fuel cells). Water can also be introduced with the feed gas. The hydrogen gas for fuel cell operation can originate from a pure hydrogen source, hydrocarbon, methanol, or any other hydrogen source that supplies hydrogen at a purity suitable for fuel cell operation (i.e., a purity that does not poison the catalyst or interfere with cell operation). Hydrogen gas electrochemically reacts at the anode to produce protons and electrons, wherein the electrons flow from the anode through an electrically connected external load, and the protons migrate through the membrane to the cathode. At the cathode, the protons and electrons react with oxygen to form water. The electrical potential across the anode and the cathode can be exploited to power an external load.
In other exemplary embodiments, one or more electrochemical cells can be used within a system to both electrolyze water to produce hydrogen and oxygen, and to produce electricity by converting hydrogen and oxygen back into water as needed. Such systems are commonly referred to as regenerative fuel cell systems.
Electrochemical cell systems generally include a number of individual cells arranged in a stack, with the working fluids directed through the cells via input and output conduits formed within the stack structure. The cells within the stack are sequentially arranged, each including a cathode, a proton exchange membrane, and an anode. Each cathode/membrane/anode assembly (hereinafter xe2x80x9cmembrane electrode assembly,xe2x80x9d or xe2x80x9cMEAxe2x80x9d) comprises a first flow field in fluid communication with the cathode and a second flow field in fluid communication with the anode. The MEA may furthermore be supported on both sides by any one of a variety of different structures disposed within flow fields defined by the particular architecture of the cell, such as screen packs or bipolar plates. These may further facilitate fluid movement to and from the MEA, as well as membrane hydration.
In an electrochemical cell system, the output pressure of the hydrogen gas can be used to control the generation rate of the cell. In such a system, a pressure transducer monitors hydrogen pressure downstream of the cell and produces a corresponding electrical signal, which is provided to analog control circuitry to control the electrical power supplied to the electrolytic cell. The analog control circuitry includes a manually-adjusted potentiometer that allows manual setting of a reference voltage corresponding to an output value (e.g., pressure). The electrical signal is compared by a comparator circuit to the reference voltage. The output of the comparator circuit is provided to a pulse width modulator that, in turn, controls a silicon controlled rectifier type power supply for the electrolytic cell. One drawback of such a manual controller is the lack of remote control of the reference voltage. Another drawback is the lack of direct integration with a feedback system.
While existing electrochemical cell system output controllers are suitable for their intended purposes, there still remains a need for improvements, particularly related to ease of use, ease of control, and feedback integration.
The above-described drawbacks and deficiencies of the prior art are overcome or alleviated by an electrochemical cell system comprising: an electrochemical cell, an energy source configured for providing a quantity of energy to the electrochemical cell; a sensing apparatus in operable communication with a gas output from the electrochemical cell, the sensing apparatus provides an output signal indicating a parameter of the gas output; and a computer in operable communication with the sensing apparatus. The computer includes a memory device configured to store a first operational parameter, and a processor configured to receive a digital representation of the output signal and the first operational parameter. The processor compares the digital representation of the output signal to the first operational parameter for regulating the quantity of energy provided to the electrochemical cell.
A method for controlling a gas output from an electrochemical cell electrically connected to an electrical source includes: sensing a parameter of the gas output to create a sensed signal indicating the parameter; retrieving a predetermined value and a predetermined variance from a memory device; comparing the sensed signal to the predetermined value; providing a signal to the electrical source when the sensed signal differs from the predetermined value by an amount greater than the predetermined variance; and adjusting an output of the electrical source in response to the signal.
In an alternative embodiment, a method of controlling a gas output from an electrochemical cell electrically connected to an electrical source includes: sensing a parameter of the gas output to create a sensed signal indicating the parameter; retrieving a predetermined upper value from a memory device; comparing the sensed signal to the predetermined upper value; providing a lower signal to the electrical source when the sensed signal is greater than the predetermined upper value; and lowering an output of the electrical source in response to the lower signal.
In another alternative embodiment, a method of controlling a gas output from an electrochemical cell electrically connected to an electrical source includes: sensing a parameter of the gas output to create a sensed signal indicating the parameter; retrieving a predetermined value from a memory device, the predetermined value indicates an expected increase in the parameter over a period of time; monitoring the sensed signal over the period of time to determine an increase in the parameter; providing a signal to one or more of an alarm and the electrical source when the increase in the parameter is less than the expected increase in the parameter.
These and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.